1. Field of the Invention
The present invention relates to electronic signal filter calibration, specifically to filters implemented on integrated circuits.
2. Prior Art
Characteristics of circuit components created in monolithic integrated circuits change with processing variations, age, and temperature. When resistance, capacitance, or inductance of a circuit component change, the frequency, phase, or amplitude response of a filter employing the circuit component changes also. Where high filtering accuracy is needed, the change in filter response may be unacceptable.
Vorenkamp et al., U.S. Pat. No. 6,549,766 entitled “System and method for on-chip filter tuning” issued Apr. 15, 2003 discloses a method for calibrating on-chip filters using a substitute filter constructed on the same integrated circuit. The substitute or dummy filter is tuned using local oscillators, then the tuned component values are frequency scaled and applied to the operative filter in the main signal path. This reference teaches that for a wide band filter amplitude response is not the optimal parameter to monitor. At the filter center frequency the top of the response curve is flat making determination of the filter center difficult. The phase response has a steep slope at the center frequency and provides an easily discernable transition for determining when the center frequency has been reached. This reference uses detection of the phase slope to tune the center of the filter.